Print heads for ejecting droplets of fluid are commonly known as inkjet print heads. Such print heads may eject fluids like ink or any other fluids having suitable properties. Droplet ejection may be generated by a number of different kinds of methods. In a particular method, a piezo actuator is actuated to generate a pressure wave in a pressure chamber that is filled with the fluid to be ejected. The pressure chamber is in fluid communication with a nozzle of the print head and due to the generated pressure wave a droplet may be ejected through the nozzle.
Commonly, the piezo actuator is arranged on a membrane, which membrane forms a flexible wall of the pressure chamber. The piezo actuator is arranged on a surface of the membrane opposite of a surface that forms the wall of the pressure chamber, i.e. the piezo actuator is arranged outside the pressure chamber, although this is not required. In order to generate the pressure wave in the pressure chamber, the membrane is deformed by the piezo actuator. The membrane is deformed at the position of the piezo actuator, but as a consequence also at the position where the membrane is clamped, i.e. at the perimeter of the pressure chamber.
In order to have a dense arrangement of nozzles for high resolution printing, it is desirable to have small structures, including a small pressure chamber. Having a small pressure chamber and consequently a small membrane results in a relatively high stiffness of the membrane. In order to be able to expel droplets, a certain volume displacement is needed in the pressure chamber upon actuation. However, in view of the desired dense arrangement, it may require a relatively large actuation voltage to deform the relatively stiff membrane such that the needed volume displacement is achieved. Using a relatively large actuation voltage on the other hand decreases the lifetime of the piezo actuator, which is of course also not desirable.
In US2008/0018204 it is disclosed to have a bending-stiffness lowering portion. Such bending-stiffness lowering portion may include thinning of the membrane or providing of a through hole through the membrane outside an area that forms the flexible wall of the pressure chamber. Thus, stiffness of the membrane is reduced and bending is eased. However, it is desirable to reduce a resistance of the area of the membrane forming the flexible wall of the pressure chamber to actuation even further.